Android and iOS device shipments are predicted to grow this year, while the number of Windows devices shipped is expected to fall slightly.

According to calculations from analyst Gartner, 866 million Android devices will ship this year (up from 505 million last year. Around 296 million iOS and Mac OS devices will ship (up from 212 million last year) while 339 million Windows devices will ship (a slight dip from 346 million last year). And next year Android is likely to see a billion devices shipped — compared to 378 million Windows devices and 354 million iOS devices.

But the raw numbers don't tell the whole story. "Although the numbers seem to paint a clear picture of who the winner will be when it comes to operating systems in the device market," said Gartner research VP Carolina Milanesi, the reality is the relevance of each operating system varies according to the type of device.

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"Apple is currently the more homogeneous presence across all device segments, while 90 percent of Android sales are currently in the mobile phone market and 85 percent of Microsoft sales are in the PC market," she said in a statement.

Still, Gartner's numbers contain yet more bad news for PC vendors, as it seems their experiments with new form factors and operating systems aren't going to stop the market for their hardware shrinking.

Shipments of traditional PCs — desktops and notebooks — are forecast to hit 305 million units in 2013, a 10.6 per cent decline from 2012. Even when ultramobiles are added to the pile (by which Gartner means devices such as Chromebooks, thin-and-light clamshell designs, and hybrid devices running Windows 8) PC shipments will still decline 7.3 percent in 2013, as consumers choose tablets.

Tablet shipments are expected to grow 67.9 percent, with shipments reaching 202 million units, while the mobile phone market will grow 4.3 percent, hitting a volume of more than 1.8 billion units.

Gartner is predicting that 20 million ultramobile PCs will ship this year — double last year. And while that number will double again to 40 million next year, that still won't be enough to offset the decline in shipments of more traditional form factors, which it calculates will drop to 289 million in next year — down from 341 million last year.

Even when designs based on Intel's Bay Trail and Haswell processors hit the market in the latter part of this year, they will only "marginally help" overall sales volumes at least initially, but may give vendor margins a boost, Gartner said.

But the tablet market is also facing some challenges, according to the analyst house, with many consumers trading down from premium tablets to more basic models.

The market share of basic tablets is expected to increase faster than anticipated, as sales of the iPad Mini already represented 60 per cent of overall iOS sales in the first quarter of 2013.

"The increased availability of lower priced basic tablets, plus the value add shifting to software rather than hardware will result in the lifetimes of premium tablets extending as they remain active in the household for longer. We will also see consumer preferences split between basic tablets and ultramobile devices," Gartner research director Ranjit Atwal said in a statement.

The bring your own device trend continues, with Gartner forecasting that 72 per cent of personal computing devices will be bought into the workplace by 2017, up from 65 per cent in 2013. "This signifies the growing importance of designing for the consumer inside the enterprise," the analyst house noted.